The placement of a luminous pyrotechnic charge on the rear of a bullet has long been used to make the flight path of a bullet visible. Because the human eye retains a visual image for approximately 1/15 of a second, a bright luminous pyrotechnic charge traveling along with a high-speed projectile appears to the observer as a luminous line which follows the flight path of the projectile.
Tracer rounds have many uses. A prominent one involves aiming a weapon by observing the flight path of the tracer round by means of its luminous trail and adjusting the gun or weapon until the trails converge with the target. In this way, it is possible to allow for relative movement between the gun and the target and such environmental factors as winds and gravity drop of the bullet. Typically tracer rounds are so employed in anti-aircraft guns which are manually aimed. Tracer rounds are likewise employed with small arms where their use may aid in teaching a marksman to accurately point the gun without aiming. For example, a number of tracer-like products have been developed for shotgun shells for use with shot rounds. Shotgun shot is normally fired at moving targets, either clay pigeons or birds on the wing. The result is insufficient time to employ conventional aiming techniques and the gun must simply be pointed and fired. The incorporation of a luminous source with the shot allows the shooter to judge the results of his efforts and so improve. Tracer rounds for rifles and pistols are often used to indicate when the magazine is empty by using a tracer round for the last round in the magazine. Tracer rounds are also used tactically: for instance, to direct fields of fire and designate targets in small arms military engagements. Tracer rounds are also used at night where conventional aiming techniques may not be possible.
Police forces may use tracers to discriminate between friendly and hostile fire. Ballistically, tracer rounds, by filling the wake of a bullet, may reduce the bullet's drag and improve its accuracy.
Game laws in many states restrict certain hunting seasons to the use of shotgun shot rounds or slugs. The result of these laws has been wide-spread interest in improving the accuracy of shotgun slugs to more nearly approach those of a conventional rifle bullet. However, hithertofor the advantages of a tracer round have not been available in shotgun slugs.
What is needed is a tracer slug adapted for use in a shotgun.